1. Field of the Invention
Erucic acid is a fatty acid which is an important raw material in the oleochemical industry. It is a component of several vegetable oils, the major industrial source of erucic acid at present being high erucic acid rapeseed oil (HEAR oil). Current methods of extraction are costly, however, and the finished product contains by-products which impart undesirable properties. Thus, there is a need for an effective, low cost method of extraction which results in the production of a high-quality product.
2. Description of the Prior Art
Erucic acid (C22:1,.delta.13) is a naturally-occurring fatty acid found in the storage triglycerides of plants of the family Brassicaceae. Rapeseed is a member of this family and is grown in several countries for its oilseed. Rapeseed oil contains a high content of erucic acid (more than 40%) and is important in industrial applications.
Erucic acid can be isolated from rapeseed oil fatty acids by fractional distillation or multiple solvent crystallization at low temperature (Stage, H., Fette Seifen Anstrichm. 1975. vol. 77, p. 165-204). In the case of fractional distillation, however, temperatures of up to 255.degree. C. must be utilized which may result in by-product formation which imparts an undesirable color to the erucic acid (Stage, H., World Conference on Oleochemicals into the 21st Century. T. H. Applewhite, ed. 1990. American Oil Chemists Society, pp. 142-160).
The search has thus continued for a process for purifying erucic acid from vegetable oils under mild hydrolysis conditions which result in a high-quality product of high yield and high purity.
It was found that lipases having fatty acid selectivity provided a milder, more convenient route to erucic acid production. Lipase from Geotrichum candidum (G. candidum), well known for its preference for C18 fatty acids containing a cis double bond in the .delta.9 position (Jensen, R. G., Lipids. 1974. vol. 9, pp. 149-157), poorly utilizes fatty acids which are longer than 18 carbons even if a cis double bond is located at the .delta.9 position in the fatty acid chain (Sonnet et al., J. Am. Oil Chem. Soc. 1993. vol. 70, pp. 1043-1045).
Lipase from Candida rugosa (C. rugosa) also exhibits some fatty acid selectivity, releasing long chain fatty acids more slowly than C16 and C18 acids from fish oil triglycerides (Lie and Lambertson, Fette Seifen Anstrichm. 1986. vol. 88, pp. 365-367; Hoshino et al., Agric. Biol. Chem. 1990. vol. 54, pp. 1459-1467). In addition, it was recently found that this enzyme hydrolyses esters containing erucic acid more slowly than those containing C16 or C18 fatty acids (Sonnet, supra; Ergan et al., Annal. N.Y. Acad. Sci. 1992. vol. 672, pp. 37-44; Kaimal et al., Biotech. Lett. 1993. vol. 15, pp. 353-356). Most fatty acids in rapeseed oil are either C18 or erucic acid. Hydrolysis of rapeseed oil with this lipase should thus result in a glyceride fraction enriched in erucic acid and a free fatty acid fraction containing only C18 acids. These fractions can be easily separated from each other, thus providing a fraction containing a mixture of the glycerides mono- and dierucin. The limited specificity of this lipase is insufficient for a commercially useful process, however, therefore studies were carried out to determine a means of enhancing the process.